Gas turbines are used in a variety of useful applications. Aviation, shipping, power generation, and chemical processing have all benefited from gas turbines of various designs. Land-based gas turbine power generation facilities can also provide combined cycle benefits when a heat recovery unit is used to generate steam from exhaust gas generated by the gas turbine and a steam turbine is operated by that steam.
In regard to general terminology, the term "gas turbine" traditionally has referred to any turbine system having a compression section, combustion section, and turbine section. In recent years, the term "combustion turbine" has become more used to reference the same machine. In this regard, this specification will use the term "gas turbine" to represent both the traditionally used term and the term "combustion turbine" as some would reference it at the present time.
Gas turbines have a compressor section for compressing inlet air, a combustion section for combining the compressed inlet air with fuel and oxidizing that fuel, and a turbine section where the energy from the hot gas produced by the oxidation of the fuel is converted into work. Usually, natural gas (mostly methane), kerosene, or synthetic gas (such as carbon monoxide) is fed as fuel to the combustion section, but other fuels could be used. The rotor, defined by a rotor shaft, attached turbine section rotor blades, and attached compressor section rotor blades, mechanically powers the compressor section and, in some cases, a compressor used in a chemical process or an electric generator. The exhaust gas from the turbine section can be used to achieve thrust, it can be a source of heat and energy, or, in some cases, it is discarded.
Some turbine sections employ the use of fluid-cooled rotor blades where either pressurized air, steam, or the like is passed through internal cooling cavities within the rotor blades used in the turbine section; this enables higher temperature output from the combustion section.
Gas turbine compressors are periodically cleaned to remove buildups of particulates on internal components. Some of this cleaning can be performed without full shutdown of the gas turbine, and materials such as water, ground pecan hulls, or chemical cleaning mixtures can be either sprayed, blown, or otherwise input into the inlet of the gas turbine after the gas turbine has been operationally configured for such a cleaning operation. At least one such chemical mixture is disclosed in U.S. Pat. No. 4,808,235 entitled "CLEANING GAS TURBINE COMPRESSORS" issued on Feb. 28, 1989 to Woodson, et al.
Other systems for minimizing buildup of particulates on internal components of gas turbines focus on cleaning of the gas turbine inlet air as is, for instance, disclosed in U.S. Pat. No. 4,926,620 entitled "CLEANING GAS TURBINE INLET AIR" issued on May 22, 1990 to Donle.
Materials such as water can also be added when the gas turbine is operating under full load to augment the power output capability of a gas turbine above the output achievable with normally humidified air; such a procedure is identified as wet compression. Wet compression enables power augmentation in gas turbine systems by reducing the work required for compression of the inlet air. This thermodynamic benefit is realized within the compressor of a gas turbine through "latent heat intercooling", where water (or some other appropriate liquid) added to the air inducted into the compressor cools that air, through evaporation, as the air with the added water is being compressed. The added water can be conceptualized as an "evaporative liquid heat sink" in this regard.
The wet compression approach thus saves an incremental amount of work (which would have been needed to compress air not containing the added water) and makes the incremental amount of work available to either drive the load attached to the gas turbine (in the case of a single shaft machine) or to increase the compressor speed to provide more mass flow (which can have value in both single shaft and dual shaft machines).
A good overview of the principles behind wet compression is found in "Water Spray Injection of an Axial Flow Compressor" by I. T. Wetzel and B. H. Jennings (Proceedings of the Midwest Power Conference, Ill. Institute of Technology, Apr. 18-20, 1949, pages 376 to 380); this article is hereby incorporated by reference herein for purposes of describing the background of this application. The article indicates that "water . . . was sprayed into the inlet duct just upstream from the compressor through four Spraying Systems type 1/4 LNN6 nozzles."
An additional incremental contribution to power augmentation is realized in the turbine section by a small increase in mass flow provided by the added vaporized liquid. A further incremental contribution to power augmentation also appears to be provided by an increase in air flow which has been noted to occur with a first, 10-20 gallon per minute, increment of water in a large land-based power gas turbine (an effect also noted in the Wetzel-Jennings article). It should be noted that additional fuel is required to raise the temperature of the cooled (respective to dry air compression) air/steam mixture discharged from the compressor to the firing temperature of the gas turbine; but the value realized from the wet compression effect is greater than the value of the additional fuel needed, resulting in value added to the operation of the system as a whole.
The power augmentation benefits of wet compression have been generally understood for some time. As noted by David G. Wilson in "The Design of High-Efficiency Turbomachinery and Gas Turbines" (1984, Massachusetts Institute of Technology), a six stage centrifugal compressor used in a 1903 vintage turbine built by Aegidius Elling injected water between compressor stages.
In the development of jet aircraft, wet compression using alcohol or water/alcohol mixtures has been of interest as a method for thrust augmentation as noted in American Society of Mechanical Engineers article 83-GT-230 entitled "Gas Turbine Compressor Interstage Cooling Using Methanol" (ASME, New York, 1983) by J. A. C. Fortin and J. F. Bardon. The FortinBardon article points to concerns with wet compression ". . . that the liquid droplets not cause serious erosion of the compressor blades."
The above comment from the Fortin-Bardon article, and another comment in the Wetzel-Jennings article that "there was no evidence of blade erosion although admittedly the tests were of short duration" help to highlight one concern regarding liquid erosion respecting wet compression that, despite the technology's very significant and long-appreciated benefits, has contributed to preventing wet compression's practical application. Indeed there are a number of risks to a gas turbine system when wet compression power augmentation is used to improve its operational performance.
As noted, one risk is derived from blade erosive effects; another difficulty (especially in large gas turbine systems) relates to localized and non-uniform cooling problems (due to non-uniform distribution of the added water) within the compressor which can distort the physical components of the gas turbine system in such a way as to cause damage from rubbing of the rotor against the inner wall of the housing and associated seals.
A further significant element of risk derives from the possibility of thermal shock if (1) the gas turbine has essentially achieved thermodynamic equilibrium under full load and (2) the liquid addition is abruptly terminated without feed-forward compensation to the energy being added to the gas turbine; the risk is derived from a potentially damaging and abrupt transient in the internal operating temperature of the turbine section if the evaporative liquid heat sink is removed in this manner.
Another element of risk is due to the possibility that components of the liquid addition system may break away and impact against the relatively delicate moving parts of the gas turbine system. Still another element of risk is established from the chance that gas turbine components will foul from impurities in the liquid added to the compression inlet air, as these impurities are deposited on the gas turbine components as a result of evaporation of the liquid in which they had been dissolved.
With particular regard to land-based gas turbine power generation facilities and chemical processing facilities, the above risk factors, the substantial investment in the gas turbines, and nonlinear, inherent scale-up considerations have collectively prevented the benefits of wet compression from being realized.
What is needed is an approach and system which enables wet compression to be pragmatically implemented in gas turbine power generation facilities and chemical processing facilities. Such a system would enable an immediate benefit to be realized from the existing base of installed gas turbine power generation facilities and chemical processing facilities. Perhaps more importantly, such a system would conceivably enable gas turbines to be optimized for wet compression at the design stage, opening new possibilities in power generation. This patent teaches such a system for enabling the use of wet compression in gas turbine systems.